Epacadostat is a selective inhibitor of the enzyme IDO (indoleamine 2, 3-dioxygenase enzyme) which is an immunosuppressive molecule expressed in cancer and dendritic cells, and selectively knocks down the expression of the gene of the enzyme IDO. It is an immune-based cancer therapy using gene silence of epacadostat in dendritic cells. Epacadostat is used for the treatment of cancers, solid tumors such as metastatic melanoma, ovarian cancer and non-small cell lung cancer. Epacadostat has the structural formula shown as Formula 1:

International patent application Publication No. WO2010/005958 disclose 1,2,5-oxadiazoles as inhibitors of indoleamine 2,3-dioxygenase and the preparation method thereof. Malononitrile, sodium nitrite and hydroxylamine hydrochloride are used as starting materials for preparation of epacadostat; and the total synthesis of epacadostat was achieved in over 10 steps. Therefore, the current synthesis method of epacadostat is still to be improved.